The present invention relates to a lamination method for laminating resin layers on a substrate, and more specifically concerns a lamination method which is preferably used for laminating a photosensitive resin layer that serves as a material for a color filter onto the substrate. The color filter is utilized particularly in the manufacture of a display panel of a liquid crystal display.
Conventionally, there has been known a method in which, upon manufacturing a display panel of a liquid crystal display, a flexible laminated film, referred to as a dry resist film, is thermally bonded (laminated) onto a substrate in order to provide a color filter on a substrate.
The dry resist film has a construction in which a photosensitive resin layer, referred to as a color resist layer, is provided on a belt-shaped support called a base film, and an intermediate layer, such as an oxygen-shielding layer, is normally interpolated between the base film and the color resist layer. The color resist layer, which is a material of a color filter, forms the color filter through exposing, developing and heating processes after the base film has been separated therefrom in the post treatment. In order to form color filters of respective colors, it is required that color resist layers of the respective colors be laminated onto the substrate; that is, for each of three colors of R (red), G (green) and B (blue), or for each of the four colors including black, processes are required in which a dry resist film is laminated onto the substrate, the base film is separated, and the color resist layer is subjected to exposing, developing and other processes so that a color filter having the corresponding color is formed.
In order to laminate the dry resist film onto the substrate, there has been known a method in which the lamination is carried out by using a device referred to as a continuous laminating device. As illustrated in FIG. 19, in the continuous laminating device, dry resist film 54 is thermally bonded continuously onto substrates 53 by a pair of thermal bonding rollers 51 and 52, while the substrates 53 are being transported between the thermal bonding rollers 51 and 52 one after another with given intervals in the direction of arrow A. The dry resist film 54 is wound onto a film take-out core 55 in the shape of a roll, and upon being thermally bonded, is supplied, with the color resist layer of the dry resist film 54 facing down so as to adhere to the substrate 53.
After the thermal bonding process, the dry resist film 54 is cut into pieces in the direction of arrow B between the respective substrates 53. Therefore, each of the substrates 53 is sent to the next process with excessive portions of the dry resist film 54 extruding in the front and rear sides when seen in the substrate-feeding direction A.
In the above-mentioned continuous laminating device, however, if the substrates 53, which are to be transported between the thermal bonding rollers 51 and 52, should be exhausted and the supply thereof should be interrupted, the next process also has to be stopped, causing unnecessary time-consuming tasks to recover the operation; the resulting problems are loss of time and loss of production.
Moreover, in the above-mentioned continuous laminating device, it is necessary to eliminate the extruding excessive portions of the dry resist film 54 for each of the substrates 53; however, it is difficult to eliminate these portions with precision, resulting in another problem.
Therefore, it has become a main trend to use a lamination method in which a device called an intermittent laminating device as illustrated in FIG. 20 is used. In the intermittent laminating device, dry resist film 59 is thermally bonded intermittently onto substrates 58 by a pair of thermal bonding rollers 56 and 57, while the substrates 58 are being transported between the thermal bonding rollers 56 and 57 one after another with given intervals in the direction of arrow C. In other words, when it is laminated onto the substrate 58, the dry resist film 59, which has been wound onto a film take-out core 60 in the shape of a roll, is cut in the direction of arrow D by a cutting means 61 so that each piece has a size shorter than length L of the substrate 58 in the feeding direction.
The following description will discuss the operation of the above-mentioned intermittent laminating device more specifically. First, as illustrated in FIG. 21(a), preparatory processes, such as clamping the leading end 59a of the dry resist film 59 and a predetermined position in the vicinity of the leading end 58a of the substrate 58 by the thermal bonding rollers 56 and 57, are carried out. Next, as illustrated in FIG. 21(b), a laminating process is started from the vicinity of the leading end 58a of the substrate 58 while the substrate 58 is being transported in the direction of arrow C. Upon laminating, the dry resist film 59 is vacuum-supported by vacuum suction units 62a and 62b for the purposes of imparting a certain degree of tension, etc.
Next, as illustrated in FIG. 21(c), in the course of laminating, the dry resist film 59 is cut by the cutting means 61 so as to have a size shorter than length L of the substrate 58 in the feeding direction. Even after having been cut, the dry resist film 59 is vacuum-supported by being sucked by the vacuum suction units 62b at the vicinity of the rear end 59b thereof so that it is free from slackness and wrinkles.
Thereafter, as illustrated in FIG. 21(d) the vicinity of the rear end 59b of the dry resist film 59 is vacuum-supported by the vacuum suction unit 62b until it has reached the limitation immediately before the completion of lamination, and as illustrated in FIG. 21(e), after having been released from the suction process, the rear end 59b is laminated onto the substrate 58, thereby completing the lamination.
Moreover, concerning another prior-art lamination method, Japanese Laid-Open Patent Publication No. 338041/1993 (Tokukaihei 5-338041) discloses a method in which upon press-bonding a laminated film onto a sheet substrate, the laminated film is press-bonded in a manner so as to extrude greatly as compared with the length of the sheet substrate.
Here, in either case of the above-mentioned lamination methods, before and after the laminating process, or during the laminating process, the film-cutting process is required. In the cutting process as described above, a cutter, such as a rotary cutter, or a special blade having a triangular edge, such as disclosed in Japanese Laid-Open Patent Publication No. 23689/1994 (Tokukaihei 6-23689), is used.
Moreover, after the dry resist film has been laminated onto the substrate, it is necessary to separate the base film located on the upper side as described earlier. Concerning such a separating method, for example, Japanese Laid-Open Patent Publication No. 157187/1995 (Tokukaihei 7-157187) discloses a method in which, as illustrated in FIG. 22, a protective film 64, laminated onto a substrate 63, is separated therefrom by using a separation needle 62. In this method, from a state in which the separation needle 62 comes into contact with the surface of the protective film 64, the separation needle 62 is lowered and pressed onto the protective film 64 as illustrated in FIG. 22(b), and in this state, the substrate 63 is moved in the direction of arrow E as illustrated in FIG. 22(c). Thus, the separation needle is allowed to stick in the protective film 64. Further, the protective film 64 on the substrate 63 is gradually separated from its end portion by moving the substrate 63 in the direction of arrow E as illustrated in FIG. 22(d).
Concerning another separating method, a method using an air knife 65 for separation as illustrated in FIG. 23 has been known. As illustrated in FIG. 23(a), in this method, an air knife 65 blows air 70 between a base film 68 and a color resist layer 69 on a dry resist film 67 that has been laminated onto a substrate 66. Thus, as illustrated in FIG. 23(b), the base film 68 is separated from the interface of the color resist layer 69.
However, the lamination method using the above-mentioned intermittent laminating device raises the following problems.
For example, in the case when the color filters of three colors, red, blue and green, are successively formed on a glass substrate used for a liquid crystal display, etc. through the lamination method using the above-mentioned intermittent laminating device, upon formation of the first color filter, bubbles 73 are entrapped between the color resist layer and the substrate 71 in a range located approximately 40 mm to 50 mm from the rear edge 72a of the dry resist film 72 on the substrate 71 as illustrated in FIG. 24.
Further, upon formation of the second or third color filter, bubbles 73 are also entrapped between the color resist layer and the substrate 71 in a range located approximately 40 mm to 50 mm from the rear edge 72a of the dry resist film 72 in the same manner as the first color filter. Therefore, as illustrated in FIG. 25, after formation of the color filter layers 74 and 75, bubbles 76 are entrapped between the color filter layers 74 and 75 as shown in FIG. 25(a) in the stripe arrangement, or as shown in FIG. 25(b) in the delta arrangement.
The reason for the generation of bubbles is explained as follows: Upon laminating the dry resist film on the substrate, as illustrated in FIG. 21(e), the vacuum support of a dry resist film 59 by the vacuum suction units 62b becomes impossible immediately before the completion of lamination, and the suction process is terminated. Consequently, a portion of the dry resist film 59, located in the region of 40 mm to 50 mm from the rear end 59b of the dry resist film 59, drops on the substrate 58 as it is, and is laminated in the state as dropped. Therefore, since no escape path for air is maintained in this portion, bubbles are entrapped therein.
Minute losses of the color resist layers measuring approximately 20 xcexcm to 30 xcexcm occur due to the generation of the bubble, resulting in problems such as color loss in the color filters. Consequently, it becomes difficult to expand the display section to the proximity of the edge of the substrate. Further, another problem is that fine contaminants, derived from the resin material, adhere to inappropriate portions.
Moreover, in the lamination method using the intermittent laminating device, upon thermal bonding, a minute amount of the color resist layer extrudes from the base film at the edge of the dry resist film; this adheres to the thermal bonding rollers, etc., causing disturbance in the uniformity of the applied pressure of the rollers, or the resin film adheres to the upper side of the base film, causing problems such as degradation in separation of the base film and the linearity precision of the edge of the color resist layer.
Furthermore, in the case when the dry resist film on the substrate is cut with a cutter, etc., after the laminating process, if the substrate is a hard substrate such as a glass substrate or a ceramic substrate, the cutter, etc., fails to cut the films repeatedly with high linearity precision, and either the substrate or the blade tends to be cracked, resulting in contaminants. These cause defects in precision devices such as liquid crystal displays.
Concerning the conventional method in which the base film is separated after the laminating process, in the case of the method disclosed by Japanese Laid-Open Patent Publication No. 157187/1995 (Tokukaihei No. 7-157187), upon sticking the protective film 64 with the separation needle 62, the separation needle 64 tends to fail to stick in the protective film 64 sufficiently, causing a problem of drop of the protective film 64. This is due to the fact that the surface of the protective film 64 is very slippery and after continuous use of the separation needle 62, the point of the separation needle 62 wears out and gradually loses its sharpness due to loads applied thereto.
Moreover, upon sticking the protective film 64 with the separation needle 62, dusts, such as film chips, are generated from the protective film 64, and adhere to the surface of the substrate 63, etc., thereby causing contamination in the manufacturing processes.
In the method in which the separation is made by using the air knife 65, upon separating, a considerable amount of air 70 is blown thereon, resulting in a problem in which defects in the products increase due to ambient contaminants involved therein.
The objective of the present invention is to provide a lamination method for laminating a resin layer such as a color resist layer on a substrate with high yield.
In order to achieve the above-mentioned objective, a lamination method of the present invention, which is a method in which a film, formed by providing a resin layer on a belt-shaped support, is cut based upon the length of a substrate in the feeding direction, and press-bonded onto the substrate, and then the resin layer is transferred onto the substrate by separating the belt-shaped support, is provided with the steps of: in the cutting process, cutting the film so that the rear end of the film, after the press-bonding, extrudes from the rear end of the substrate by a predetermined width; and cutting the film again at a position inside the rear end of the substrate prior to separating the belt-shaped support after the film has been press-bonded so as to eliminate the portion of the film extruding from the substrate.
This method makes it possible to prevent bubbles from being entrapped onto the interface between the substrate and the resin layer; therefore, it is possible to reduce the number of defective products, and also to expand the display section to the vicinity of the edge of the substrate. Moreover, since this method reduces the possibility of the resin layer extruding even at the cut section on the substrate, the belt-shaped support can be separated easily from the resin layer along the interface, making it possible to laminate the resin layer on the substrate with high linearity precision.
Moreover, in order to achieve the above-mentioned objective, another lamination method of the present invention, which is a lamination method including a process in which, after a film, formed by providing a resin layer on a belt-shaped support, has been press-bonded onto a hard substrate, one portion of the film on the substrate is cut, is provided with the step of using a shaving-use blade made of stainless steel in the cutting process.
With this method, upon cutting the film on the substrate, it is possible to reduce the occurrence of scattering and unevenness of resin, and consequently to allow cutting with superior linearity precision and easy separation. Further, even in the case of a hard substrate, both the substrate and the blade become less susceptible to cracks; therefore, since the blade can be used repeatedly while maintaining a superior cutting property, high production efficiency is ensured.
In order to achieve the above-mentioned objective, still another lamination method of the present invention, which is a lamination method in which, after a film, formed by providing a resin layer on a belt-shaped support, has been cut based upon the length of a substrate in the feeding direction, and press-bonded onto the substrate, the resin layer is transferred onto the substrate by separating the belt-shaped support, is provided with the steps of: in the separating process, making at least one cut from one end of the film and separating the belt-shaped support by making the belt-shaped support and the resin layer apart from each other at the vicinity of the cut.
In this method, a minute rise is formed between the belt-shaped support and the resin layer by making the cut in the belt-shaped support so that a load applied upon starting the separation of the belt-shaped support is dispersed and lessened, thereby allowing easy separation. Moreover, since the separation is gradually extended from the cut area, it is carried out easily without difficulty.